From the start, Sousuke just knows that Rin will be much more than just a friend or a best friend. Being with him is like breathing – easy and natural and so right. It's only when Rin's gone that Sousuke feels the horror of his absence for the first time, feels the pain like he's bleeding slowly from a wound that he can't find. When did it begin, he wonders, the comforting sense of familiarity that blooms every time he sees Rin's face or hears Rin's voice or even smells Rin's particular salty, chlorine-reminiscent scent?

-o-o-o-o-

Maybe it begins with Rin's exuberant introduction, with his disarming grin and that cocky tilt of his head as he surveys the room, wine-red eyes piercing as they meet Sousuke's bottle-glass blue-green eyes and then, that secret thrill that blooms in Sousuke's stomach, excitement and apprehension and joy all rolled into one emotion. Like freefalling into an open sky, Sousuke thinks later, or feeling the wind whip against his face.

In class, Sousuke doodles restlessly on his finished assignment, feeling the draw of the new student across the room even as he fights to keep his eyes focused on his own paper instead of letting them drift to Rin and the shockingly vivid red shade that his hair becomes in the sunlight. Class seems to drag on forever until they are dismissed and then there's a small hand waving in front of Sousuke's face and Rin's bright voice asking him whether he's in the swim club.

"I could tell from your goggle tan!" Rin says excitedly and Sousuke feels himself smiling.

"Yeah, we only practice in an outdoor pool." Sousuke says, deciding to leave out the fact that his mother had pushed him into swimming after he had nearly drowned as a kid and that even though swimming came naturally to him it was a struggle for him on his best of days to get into the wintry pool at 5 a.m. in the morning. He brushes away the memories of the swim pool, a place where he feels empty because he's always practicing hard and keeping to himself while the other kids splash each other because swimming is all fun and games for them but it's work for him, has always been work for him.

"I want to join!" Rin stops and stares at Sousuke for a moment and Sousuke has an eerie feeling that Rin can see right through him, that he can see the boy who had once spent an entire morning watching a single balloon float away unhindered into the endless sky. "We can swim together!"

Then class starts again and it's a drag until the end of the day when afternoon practice starts and Rin is there, snapping his goggle straps against the back of his skull and Sousuke almost flinches at the sharp sound but Rin just smiles a bit competitively, baring pointed teeth, and executes a perfect start into the pool.

Sousuke watches in poorly concealed wonder. For the first time he begins to see how swimming might be beautiful, because when Rin swims it's like he conquers the water, pulls and pushes and rides it as effectively as any shark, and for a startling second he feels a fierce desire to swim like Rin does.

"What's wrong?" Rin has returned to the edge of the pool where Sousuke still waits and his eyes are on Sousuke. Concerned, curious. "Aren't you getting in?"

Sousuke feels the corner of his lips curl into an answering smile and he hates swimming a little less. "I am now."

From then on they are inseparable, as they both discover that they share the same dislike for breaststroke kickboard drills and the same affinity for butterfly and Sousuke meets Rin's little sister when he attends a sleepover at Rin's house and he's never had that experience before, never had anyone who wanted to be his friend enough to invite him to anything and Sousuke is glad and bizarrely grateful that it was swimming of all things that has brought them together.

-o-o-o-o-

They share their dreams, memories, and fears.

Sousuke tells Rin about the time he had friends, how he used to hang out with a group of boys in swimming but one of the boys was always jealous of him for some reason and eventually excluded him from the group; Rin threatens to punch the guy until Sousuke shakes his head and says that it doesn't matter, that he's glad because he has Rin and he really doesn't need anyone else.

In return, Rin confides in Sousuke about his father's death and his father's dreams passed down to him and Sousuke sees Rin cry for the first time and the sight tears into him sharper than any knife and then he's crying too and hugging Rin until Rin's breaths no longer hitch and sobs no longer shake his slender frame. Rin thanks him for being there and Sousuke can only promise that he will always be there because they are best friends, aren't they?

Then they both talk about how amazing it would be if they could swim in the Olympics and Sousuke agrees because his love of swimming, inspired by Rin, has grown stronger even as their friendship has grown closer. But mostly Sousuke thinks that it would be wonderful to swim with Rin by his side, because without Rin what meaning would it have?

-o-o-o-o-

It is Sousuke who comes up with the idea of a secret handshake but it is Rin who takes the idea and runs with it, appearing the next day with a handful of ridiculous motions in mind. Sousuke has to laugh in exasperation at Rin's excitement and they spend their whole lunch arguing until they both decide on a handshake that is simple enough that they won't forget it the next day.

They swim a relay for the first time and even though they had lost they were a team and there is nothing else like the feeling of seeing Rin soar above him as Sousuke touches the wall and gasps for air after swimming a 50m butterfly because Rin had insisted that Sousuke take his favorite stroke. Then afterwards they do their secret handshake while the rest of the team watches in consternation and then Rin's hugging him again and bragging about the awesome relay and all Sousuke can think about is Rin's steady warmth, his breath in Sousuke's ear. How Rin smells like freedom.

When Rin's arms loosen around him Sousuke is loath to let go.

-o-o-o-o-

But everything changes after their relay against Nanase Haruka.

At first Rin is nonchalant. "Ah, well." His words are light and his tone casual. "We tried our best, didn't we?"

But Sousuke sees the way that his eyes linger on Nanase's back as he exits the pool, and for some reason Sousuke suddenly feels tense, on edge. His fists clench, then relax. He doesn't like it, but there really isn't anything he can do about it.

"Yeah, we did. We just have to work harder next time." Sousuke says dryly, trying to contain the bitterness that is rising within him. "You seemed awfully distracted during your part though."

Rin flushes in embarrassment. "Yeah, well, he was a good swimmer." Then he glares. "You're one to talk. What was up with the kickstart at the beginning of your race?"

Sousuke lets him change the topic, mostly because he already hates the longing glance that Rin is throwing at the pool; he's known Rin for long enough that he knows that Rin is remembering the race and then he realizes with a sudden chill that Rin has never been one for idle distractions; when Rin wants something he works at it wholeheartedly and his newest obsession just might be Nanase.

After that Rin doesn't want to swim butterfly anymore; he wants to focus on freestyle. And Sousuke begins to notice that at every swim meet Rin scans the crowd eagerly for a particular dark-haired, blue-eyed kid, his eyes darkening in disappointment when he doesn't catch any glimpses of Nanase. When he does see him he often begs Sousuke to stay a just little longer after both their events have ended so he can watch Nanase swim.

Sousuke could never say no to those pleading eyes so he nods yes even as he frowns and faces the pool to watch Nanase as Rin wants him to. Nanase's style is different than Rin's aggressive style: he's graceful. He moves like a dancer in the water. He flows and bends and strokes and moves like he was born to be in the pool and Sousuke catches Rin drinking in that sight like a wanderer dying of thirst in the desert.

Rin's eyes shine as he turns back to Sousuke. "Wouldn't it be awesome to swim like that, Sousuke? He swims so beautifully..."

Sousuke nods absently, even as he thinks silently to himself that he far prefers the way Rin swims, the way Rin throws himself at the water in his passionate, almost desperate style.

-o-o-o-o-

It isn't long after that when Rin announces that he is transferring to Iwatobi Elementary School because he has found someone that he wants to swim in a relay with. Sousuke instantly thinks of the kid that Rin is always watching. "It's Nanase, isn't it?" He says without thinking, and glances up just in time to see Rin's surprised look like a slap in the face.

"Yeah. How did you know?" Rin asks, and Sousuke can feel nothing but dumbfounded incredulity. How can he not know, when his best friend is as distant as the birds in the sky when they swim together, when their conversations have turned into nothing but one continued monologue about catching up to Nanase Haruka and when Sousuke has woken up five times in a row in a cold sweat after dreaming of Rin drowning as he chases after Nanase's disappearing shadow? How can he not notice, when he pays even closer attention to his best friend than Rin pays to Nanase?

"It was pretty obvious." Sousuke laughs instead and feels the tension in the air clear as quickly as it had descended upon them. "So you're moving?"

"No, just transferring schools. My sister's staying at this school." Rin kicks idly at a rock by his feet. He seems to remember that Sousuke is still watching him and looks up quickly. "I'm not leaving you behind, I'd never do that! We can still hang out together every day, after practice!" He is smiling but Sousuke thinks that he can see in Rin's eyes a quiet plea for understanding. And Sousuke understands. He really does. This obsession is something that Rin needs to get over, that he needs to conquer and then move on. And then he'll come back. They will always be best friends, anyways. There isn't a thing that Sousuke thinks can tear them apart.

So Sousuke just nods again. "I understand." He says, quiet and accepting, the way he has always been. He's the solid, responsible one, the one that people can always rely on, steady as a rock, weathering the countless currents and ripples of his friendships, of other people's errant emotions. He's so different from Rin that sometimes he wonders how they had become friends in the first place. Rin is bright, spontaneous, passionate, charismatic. He races through people's hearts like a spark, always encouraging, sassy, contemptuous, superior. Rin is full to the brim with easy charm and self-possession and has never doubted for an instant that he is one of the best swimmers out there, until he met Nanase, that is.

But out of all the people in this school Rin has chosen Sousuke as his best friend, and Sousuke only has to wonder why to realize the reason: because they understand each other so completely. So much so that even though Sousuke wants to say something to express his own bitterness, he can't. Because he can understand why Rin wants so badly to prove to himself that he is just as good as Nanase, and how naturally Rin will do anything to chase after his dreams, including transferring to Iwatobi Elementary School. Including leaving Sousuke behind.

And then Sousuke has to wonder just how completely Rin understands him, because isn't what Sousuke wants just as important as what Rin wants?

-o-o-o-o-

For awhile they keep it up. Rin visits him regularly outside of school and they talk about various things. They hang out at Rin's house, or Sousuke's house sometimes to get away from Rin's slightly annoying little sister, or they go shopping for new swimsuits or they visit the zoo but they hardly ever swim together anymore for some reason. Their conversations are still peppered with mentions of Nanase - "Haru stripped in the field trip to the aquarium today!" - but Sousuke is willing to put up with it to spend time with Rin. Rin is considerate, asking about his old teammates at Sano Elementary, but anyone can see that his heart isn't in it. His heart is in the pool with the rest of his new teammates at Iwatobi, with the sunny Hazuki Nagisa and thoughtful Tachibana Makoto and most of all with the silent prodigy that Rin now calls Haru, of all things.

They do their handshake and Sousuke's pleased at the familiarity in Rin's movements until Rin pauses with an odd expression on his face and says that he has to go because his team had decided on some night swimming to practice for their next relay and Sousuke assures him that he understands.

The door shuts behind Rin with a careless slam and Sousuke doesn't get up from his seat to watch Rin go because he's sick of watching Rin's departing back.

-o-o-o-o-

Time passes. They still hang out but not as often. Rin teases Sousuke about the girls that are always hanging around him; Sousuke scoffs. He searches for things to say but comes up with nothing. He's tired of talking about the Iwatobi swim team. He's tired of not being able to say what he wants. Their conversations are circles that always end up in the same place: on Nanase.

"Why don't we swim?" He suggests, and Rin's eyes glint in the dim light.

"I bet I'm faster than you now."

Sousuke relaxes. This is familiar territory. "You wish."

They get in the pool and race, first in a 50m butterfly, and then in a 50m free. Sousuke is faster in butterfly, but Rin is faster at free.

"Haha!" Rin crows, pumping his fists in the air, "I told you I was better!"

"I beat you in butterfly." Sousuke reminds him, carefully examining Rin's expression.

Rin doesn't seem to mind. "Well," he points out, "I was a whole two seconds faster than you at free." His face darkens. "I'm still not as fast as Haru though."

Sousuke mentally sighs. There's just no avoiding the topic of Nanase. "Just work harder." He feels tired. "You'll catch up eventually."

Rin frowns. "What if I can't?"

You might never be able to, Sousuke wants to say. Rin is very good at swimming, but Nanase was born to swim. Instead he tries a reassuring grin. "You can," Sousuke punches Rin's shoulder. "I know you can."

Rin's smile is grateful and Sousuke feels his heartbeat quicken so he adds, "Only so we can swim together in the Olympics and then I'll beat your butt so hard you'll go crying back to your mother."

"You wish!" Rin laughs and they race back to the locker room.

-o-o-o-o-

When Rin's team wins the relay Sousuke wants to feel happy for his best friend as he watches them hug from the lane next to them. His own team takes second place and Sousuke doesn't mind because Rin is happy and it's been a very long time since he's seen Rin smile like that. The last time was the time they snuck out of Rin's house during a sleepover to have a midnight swim. Sousuke wonders idly how this relay experience compares to that.

Sousuke's there, off to the side, as the winning team takes a photo and he misses Rin's wave at him so when he turns around he is surprised to see Rin standing right there and then Rin is hugging him, animated and euphoric, "We won, Sousuke! Did you see us? We won!"

"Congrats." Sousuke replies, and then Rin releases him and bounces back to the team and they're all laughing and Sousuke won't admit it to himself, but not for the first time he feels very left out. Shivering now that the race is over, he gathers his clothes and towel and heads home.

-o-o-o-o-

Three days later Rin knocks at Sousuke's door. "I'm moving."

"Where?" Sousuke asks, and then his stomach is dropping, plummeting to the floor at Rin's answer of Australia.

Sousuke grips the door handle tightly. He needs an anchor. "Why?"

"It's a swim school." Rin says, "I'm getting closer to my dream."

Sousuke smiles. "I'm happy for you. I really am."

Rin bites his lower lip. Sousuke winces at the thought of those sharp incisors. "I'll miss you."

"You better write." Sousuke says, low and fierce, because his friendship with Rin is the one thing that he won't give up on, that he'll always fight for.

"I will!" Rin brightens. "And I'll beat them all and when I come back, I'll be the fastest swimmer that Japan has ever seen!"

"I know you will." Sousuke steps back. "Hey, best friends forever right?"

They do the handshake and Rin for once doesn't mention Haru at all as he steps forward and gives Sousuke a long hug, and then he's gone and Sousuke doesn't hear from him for a few months.

-o-o-o-o-

On New Year's Eve Rin is at his door with a present and they reminisce for a few hours and Rin apologizes for not writing, but he's just so busy learning English and swimming and keeping up with his schoolwork that he's simply forgotten. Sousuke says it's okay, that he understands, and asks Rin how fast he's gotten.

"Very fast." Rin replies, but Sousuke spies a flash of uncertainty in his best friend's eyes.

Sousuke stares at the wrapped present on his table. "I bet you're the fastest swimmer there."

Rin says nothing. It hurts Sousuke to see this Rin, with his faith in himself shaken. He chances another glance; Rin's staring into the distance. He looks so lost and vulnerable, like a child. Sousuke sighs.

"I'd better go." Rin says finally. "I have to spend the rest of New Year's Day with my family."

After he leaves, Sousuke unwraps the present. It's a framed photo of the two of them by the pool, clutching their respective gold medals, both wearing wide grins. Rin's teeth sparkle in the light, his head thrown back mid-laugh. He has an arm casually slung around Sousuke's shoulders. Sousuke carefully places the photo on his desk where he'll be able to see it every day. He stares at the photo and his throat closes with some ineffable emotion.

-o-o-o-o-

He doesn't hear from Rin for a whole year, not even on New Year's Day when he knows that Rin is on break.

-o-o-o-o-

Sousuke is surprised to receive the letter. Reading the letter is like receiving a kick in the shins - Rin's hurting, more than he'd thought, and he's never been able to stomach the thought of Rin's pain. The helplessness that sears through him is the worst thing that he's ever felt, and Sosuke has to put the letter down for a moment to collect his thoughts. Then, unable to help himself, Sousuke reads the letter again, only stopping after he notices all the smudges where all of the you's had been erased to write Haru. For a second he can't breathe, as the weight of this hits him, presses him down like gravity does. Betrayal tastes like salt in his mouth, or blood, Sousuke can't decide which. He carefully refolds the letter and places it back into the envelope. Sousuke goes on a walk to calm himself and when he returns he knows what he has to do.

At the next meet, Sousuke swims the 50m freestyle against Nanase. He's not surprised when he loses, but he uses the chance to examine Nanase again, the way he moves in the water. Nanase, Sousuke decides, is a cold swimmer. He's aloof and bored and his stroke, although graceful, is as impassive as the rest of him. He lets the water isolate himself from the rest of the world. Despite this it's still a thrill to swim against him, and for a second Sousuke can almost see how Rin had become so obsessed. Then the race is over and Nanase climbs out of the water and only tilts his head curiously when Sousuke hands him the letter.

"It's from Rin." Sousuke explains.

Nanase blinks. A tall boy, Tachibana, comes up to him and hands Nanase a towel. "Hey," Tachibana says to Sousuke. "You were pretty fast."

Sousuke glances at the swimming scoreboard. "Nanase-san was much faster."

"Still, you did well." Tachibana insists, and Sousuke nods politely. Sensing that Sousuke has nothing else to say, Tachibana glances between him and Nanase and smiles. "I'll wait in the showers, okay?"

Nanase inclines his head slightly and they both watch as Tachibana enters the locker rooms.

"Rin's in Australia." Nanase says, face expressionless.

Sousuke feels a prickle of irritation. "I know."

"You're his best friend." Nanase's voice is low.

"He told you?"

Nanase's gaze drops to the floor. He speaks quietly, almost in a whisper. "He quit swimming."

"What?" Sousuke can't believe his ears.

"We raced and he lost."

Sousuke wants to grab Nanase by the shoulders. He wants to shake Nanase. Rage rises in him like fire in his stomach and he wants to shout, how can Nanase do this to Rin? Swimming is Rin's dream, has always been Rin's dream. But he controls himself, watches Nanase retreat. His fingers tremble in anger, but he stalks away before he does something he will regret. I hate you, he thinks vehemently towards Nanase. It's the first time he's admitted it to himself, that he hates Nanase for taking Rin away from him. That it's never been the same since Nanase has entered their lives like a parasite leeching into every conversation.

Sousuke has never been the impulsive type, but he's come to learn that the normal rules of his life don't apply to Rin. Rin's not just another person, Rin is a part of him. Like his alter ego, almost. And Sousuke will do whatever it takes to protect him.

-o-o-o-o-

At the next swim meet Nanase is not there. Sousuke listens to the gossip and learns that Nanase has quit swimming competitively. Serves him right, he thinks, but then his thoughts drift to Rin and he can't help but worry.

-o-o-o-o-

They haven't talked in four years. Sousuke isn't really keeping track by this point but he continues to work diligently during practice because that's what Rin would expect of him and he's swimming for both of them now, swimming to reach the Olympics like he'd promised Rin. He hopes that Rin has taken up swimming again, that Rin is fulfilling his part of their promise, but there's no way of knowing since he's sent a total of three letters and gotten replies to none of them so he figures that either the mail has gotten lost or Rin is too busy or he's moved somewhere else and not told Sousuke.

By this time Sousuke has tons of teammates and friends and even a few ex-girlfriends and his mother has told him that it is a bit silly of him to hang onto a childhood friendship like a dog faithfully hanging onto an old bone but none of them understand. They don't understand how Rin was the first or how he's left an indelible tattoo on Sousuke's heart; they don't know how Sousuke and Rin understand each other or how they shared so much with each other that they could practically read each other's mind. But sometimes Sousuke catches himself and realizes that he hasn't spared a thought to Rin for nearly a month and he hates himself a little bit because really, how could he forget?

And sometimes he wonders if Rin has forgotten him. But it hurts too much to think of it so he usually thinks of something else instead, like swimming, or how fast Rin will be when he returns to Japan.

-o-o-o-o-

Sousuke gets scouted and the first thing he thinks of is Rin, how happy Rin would be for him. He sends another letter to Rin but this one is returned unreceived with a note saying that the student requested no longer attends school there.

-o-o-o-o-

At the meet he's startled when he hears Rin's name being announced. "And in lane 4, Matsuoka Rin from Samezuka Academy..."

So Rin was back in Japan. And he hadn't told Sosuke, damn him.

Sousuke been preparing to warm up for the relay but after hearing Rin's name he can't help but climb out of the water and head to the tents bordering the pool where the swimmers are competing. He sees Rin struggling and the old helplessness rises in Sousuke again and Sousuke then happens to look up right at Nanase, who is perched in the stands and staring at Rin, for once not wearing his customary stony expression. Right away the helplessness turns into rage because it can't just be a coincidence, that Nanase is here at the meet and that Rin is losing spectacularly at one of his best events and that again, Sosuke can't do anything about it.

During the relay Rin swims for the Iwatobi swim team and they all look disgustingly happy even though the team gets disqualified and Sousuke feels a trickle of unease because just who is Nanase and why does he think he can just drag Rin into this mess, and why can he make Rin so happy when Sousuke hasn't been able to bring a smile to Rin's face in years?

It must be Nanase's fault because it always is. Since the very first time Rin raced against Nanase, Rin's been drifting away from Sousuke.

That evening Sousuke tells his mom that he wishes to transfer to Samezuka Academy. Nanase doesn't even go there and Sousuke's losing the battle to him but Sousuke will never stop fighting because Rin belonged to Sousuke long before they'd ever met Nanase and he just can't let that go.

But Sousuke is confident that he can make it work. After all, they are best friends forever, aren't they?

-o-o-o-o-

And he's right.

When they do their familiar handshake and he glances up into Rin's smiling eyes, it is like coming home for the first time.